KR20200087422A - a auto offset compensation device based binary searching of pulse oximeter - Google Patents

Abstract

The present invention relates to a binary search-based automatic offset correction device for an oxygen saturation meter. According to the present invention, an ambient signal attributable to ambient light is removed during amplification processing of a pulse-type input signal driven by an optical signal such as oxygen saturation and pulse oximeter, and thus a high signal-to-noise ratio can be obtained. The present invention includes: an LED drive unit for current generation; a light-emitting unit emitting light by receiving the current generated by the LED drive unit; a detection unit detecting the light reflected by a blood vessel in a finger near the light-emitting unit, converting the light into a current, and outputting the current; a current-voltage conversion-amplification unit receiving the current converted by the detection unit, converting the current into a voltage, and amplifying and outputting the voltage; a sampling-filtering unit receiving the voltage converted and amplified by the current-voltage conversion-amplification unit and sampling, filtering, and outputting the voltage; a digital conversion unit receiving the voltage filtered by the sampling-filtering unit, converting the voltage into a digital value, and outputting the value; a comparison unit receiving an output signal of the current-voltage conversion-amplification unit and comparing whether the signal is a positive number or a negative number; a binary search logic unit searching for a value of the output signal of the current-voltage conversion-amplification unit close to 0 using binary search logic in accordance with the comparison result of the comparison unit; and a current conversion unit converting the search value of the binary search logic unit into an analog value and outputting the value to the current-voltage conversion-amplification unit.

Description

{A auto offset compensation device based binary searching of pulse oximeter}

The present invention relates to an oxygen saturation meter, and in particular, to an automatic offset correction device based on the binary search of the oxygen saturation meter to automatically obtain the high signal-to-noise ratio by automatically removing the offset component due to the ambient signal.

As personalization and aging progress, individuals take regular health checkups with an interest in their own health. However, since the inconvenience of having to take a separate time for health check-ups comes, most of them go to the hospital when health problems occur. However, in the case of an elderly person or a disabled person with mobility or disability, it is inconvenient to go to the hospital and it is necessary to grasp the state of the body (that is, the biological state) from time to time to cope with the dangerous situation.

Therefore, oxygen saturation measurement is frequently used as a measurement target for personal health. Oxygen saturation is measured non-invasively by measuring the light absorption by wavelength of the pulsating component of arterial blood to calculate the oxygen saturation (SpO2) in the blood.

In general, in order to measure the oxygen saturation in the heart rate and blood vessels using an optical signal, a method of illuminating the light of the LED on the blood vessel and measuring the light sensed by the detection unit of the light receiving unit is used. At this time, in processing the light input signal of the light receiving unit, the quality of signal processing is often deteriorated due to ambient light that is much larger than the amount of light to be measured according to the on/off of the LED. To solve this, techniques for removing ambient light are applied when implementing a heart rate and oxygen saturation measurement system.

In the case of US 5954644 in the prior art, in the measurement of photoplethysmography (PPG), when LED is off, ambient light is sampled and held, and the LED is turned on to sample and hold the PPG signal to add two signals. Is used to remove ambient light by amplifying at the differential amplification stage.

In the case of US 8315684 of the prior art, in order to remove ambient light of an oximeter for implementing PPG or oxygen saturation (SpO ₂ ), when driving an infrared (IR) LED, a light input signal, when driving a red LED (Red) To convert the ambient light input signal when the LED is off, the ambient light input signal (ambient) to digital using the sigma-delta interface, and remove the ambient light signal from the microcontroller stage. Apply techniques.

Among the prior arts, in the case of an ambient light removal technique using an additional differential amplifier used in US 5954644, etc., an amplifying unit for removing ambient light is added, which is inefficient in terms of power consumption and size of the circuit. In addition, there is a limitation that only ambient light below the input range of the additional differential amplifier can be removed.

In the prior art, since the ambient light removal technique in the digital domain used in US 8315684, etc. removes ambient light through digital signal processing, when the signal of ambient light is large, among the digital signals converted through the analog/digital converter There is a disadvantage that the specific gravity of the ambient light is increased, the dynamic range of the signal to be actually acquired is reduced, and the signal-to-noise ratio is reduced.

The present invention has been devised to solve the above problems, and when amplifying and processing a pulse-type input signal driven by an optical signal such as a pulse oximeter or oxygen saturation, the background signal due to ambient light (ambient) The object of the present invention is to provide an automatic offset correction device based on a binary search of an oxygen saturation meter that obtains a high signal-to-noise ratio by removing signals.

The automatic offset calibration device based on the binary search of the oxygen saturation meter according to the present invention for achieving the above object is an LED driving unit for generating a current, a light emitting unit for receiving the current generated from the LED driving unit and emitting light, to the light emitting unit A detection unit that detects light reflected from the blood vessel inside the finger and converts it into a current, outputs the current converted by the detection unit, converts it into voltage, amplifies and outputs it, and the current-voltage A sampling and filtering unit that receives the converted and amplified voltage from the conversion amplification unit and samples and filters it, and a digital conversion unit that receives the filtered voltage from the sampling and filtering unit and converts it to a digital value and outputs the current. -A comparison unit that receives the output signal of the voltage conversion amplification unit and compares whether it is positive or negative, and performs a binary search logic according to the comparison result of the comparison unit. It is characterized in that it comprises a search logic unit, and a current conversion unit for converting the value retrieved from the binary search logic unit to an analog value and outputting it to the current-voltage conversion amplification unit.

The automatic offset correction device based on binary search of the oxygen saturation meter according to an embodiment of the present invention has the following effects.

That is, a high signal-to-noise ratio can be obtained by removing an ambient signal caused by ambient light when amplifying and processing a pulse-type input signal driven by an optical signal such as a pulse oximeter or oxygen saturation. have.

1 is a block diagram schematically showing an automatic offset calibration apparatus based on binary search of an oxygen saturation meter according to the present invention.
FIG. 2 is a flowchart illustrating an operation of the turnover search logic unit of FIG. 1.
3 is a circuit diagram illustrating the binary search logic unit of FIG. 1.
4 is an operation timing diagram of the binary logic operation unit 3

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present invention pertains may easily practice. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. In addition, in order to clearly describe the present invention in the drawings, parts irrelevant to the description are omitted, and like reference numerals are assigned to similar parts throughout the specification.

Throughout the specification, when a part is "connected" to another part, this includes not only "directly connected" but also "electrically connected" with other elements in between. . Also, when a part “includes” a certain component, this means that other components may be further included instead of excluding other components, unless otherwise specified.

The oxygen saturation meter according to an embodiment of the present invention measures oxygen saturation by using a photoplethysmogram (PPG) sensor. The measurement of oxygen saturation using a light volume pulse wave sensor uses a method of acquiring a signal using a linear relationship between the volume of blood that changes due to contraction and relaxation of the heart and the amount of light absorbed by hemoglobin in the blood. By measuring the change in infrared light intensity using, it is generally measured on fingers, wrists, toes, ear balls, etc.

In the following embodiment, a case in which oxygen saturation is measured in a finger will be described as an example. In addition, the oxygen saturation meter according to an embodiment of the present invention uses a Zigbee wireless communication module that uses a 2.4 GHz ISM band region to prevent patients and doctors from being spatially constrained, so that the results of oxygen saturation measurement can be remotely performed. To be transferred to.

1 is a configuration diagram schematically showing a binary offset-based automatic offset calibration device of the oxygen saturation meter according to the present invention.

The automatic offset calibration device based on binary search of the oxygen saturation meter according to the present invention, as shown in Figure 1, LED driving unit (LED driving circuit) 110 for generating a current, and the current generated from the LED driving unit 110 A light emitting unit (LED) 120 for receiving and emitting light, a detection unit 130 for detecting light reflected from the blood vessel inside the finger A approaching the light emitting unit 120 and converting it into a current, and outputting the converted light The current-voltage conversion amplification unit 140 that receives the converted current from 130 and converts it into a voltage and amplifies the output, and receives the converted and amplified voltage from the current-voltage conversion amplification unit 140 to sample and A sampling and filtering unit (150) for filtering and outputting, and a digital conversion unit (ADC) (160) for receiving the filtered voltage from the sampling and filtering unit 150 and converting it to a digital value for output. , The comparison unit 170 compares whether the output signal (Vout) of the current-voltage conversion amplification unit 140 is positive or negative, and compares the binary search logic according to the comparison result of the comparison unit 170. The binary search logic unit 180 searches for a value in which the output signal Vout of the current-voltage conversion amplification unit 140 approaches O, and the value searched in the binary search logic unit 180 is analog. It is configured to include a current converter (Current DAC) 190 that converts to a value and outputs (iDAC) the current-voltage conversion amplifier 140.

The automatic offset calibration device based on the binary search of the oxygen saturation meter according to the present invention irradiates light (eg, LED light) to the user's finger (A) and receives light transmitted through the finger (A) through the PD (detector) , Oxygen saturation is measured using the received light.

The automatic offset calibration device based on binary search of the oxygen saturation meter according to the present invention configured as described above generates a current required by the LED driving unit 110 and supplies it to the light emitting unit 120, and the light emitting unit 120 is the LED Light emission through the current supplied from the driving unit 110 illuminates the blood vessel inside the finger A.

When the blood vessel inside the finger is illuminated through the light emitting unit 120, the light reflected from the detection unit 130 made of a photodiode is detected, converted into a current, and output. At this time, the current output from the detection unit 130 is generally driven in the form of a pulse. Accordingly, the current-voltage conversion amplification unit 140 converts the voltage to a voltage and amplifies the output.

The voltage converted and amplified through the current-voltage conversion amplification unit 140 is received from the sampling and filtering unit 150, sampled and filtered at an appropriate timing, and the voltage is digitalized again using the digital conversion unit 160. Convert to a value.

Here, the current-voltage conversion amplification unit 140 is configured in a fully differential type, and compares whether the output signal Vout of the current-voltage conversion amplification unit 140 is positive or negative in the comparator 170. Then, based on the result transmitted through the comparison unit 170, the binary search logic unit 180 retrieves the digital value of the output signal of the current-voltage conversion amplification unit 140 close to 0, and the binary The current conversion unit 190 converts the digital current value searched through the search logic unit 180 into an analog value, and outputs it to the current-voltage conversion amplification unit 140.

The automatic offset calibration device based on binary search of the oxygen saturation meter according to the present invention will be described in more detail as follows.

The control signal for driving the LED driving unit 110 to supply the current required to drive the light emitting unit 120 is called LED_ON. The total current flowing through the detection unit 130 is iPD, the ambient light current component flowing through the detection unit 130 due to ambient light is iAMB, and the reflected light current flowing through the detection unit 130 due to vascular reflected light for measuring a photoplethysmogram. Assuming that the component is iPPG, the output current of the current converter 190 is iDAC, and the current flowing through the feedback impedance Zf of the current-voltage converter amplifier 140 is iOUT, the following equation is summarized.

That is, iPD is the sum of iAMP and iPPG, and iOUT is the sum of -iPD and iDAC.

When the LED_ON=0, which is the control signal of the light emitting unit 120, no current flows through the light emitting unit 120, and the reflected light current component iPPG flowing through the detection unit 130 becomes 0 and the current flowing through the detection unit 130 iPD is as shown in Equation 2 below.

Accordingly, the output current iDAC of the current mode DAC of the current converter 190 is adjusted so that Vout is the closest value to 0 through the binary search logic unit 180. Assuming that the output signal Vout = 0 of the current-voltage conversion amplifier 140 is the binary search, iDAC = iAMB.

Then, when the control signal of the light emitting unit 120 is set to LED_ON = H, the total current iPD flowing through the detection unit 130 has both the ambient light current iAMB and the reflected light current iPPG. At this time, since the current converter 190 generates a current corresponding to the ambient light current iAMB, the output current iDAC of the current converter 190 becomes the same as the ambient light current iAMB.

The output voltage Vout of the current-voltage conversion amplifier 140 when the control signal LED_ON = H of the light emitting unit 120 is as shown in Equation 3 below.

Therefore, only the signal corresponding to the reflected light current iPPG to be measured without the component due to the ambient light current iAMB can be measured at Vout, and the digital conversion unit extracts the desired signal from the sampling and filtering unit 150 with the LED_ON signal and appropriate timing. By operating 160), only the desired reflected light current iPPG component can be digitally converted and output.

The current-voltage conversion amplification unit 140 may be driven in the form of various timing signals, and appropriate timing sets the LED_ON signal, which is the driving signal of the light emitting unit 120, to H, and the current-voltage conversion amplification unit ( After the stabilization time of 140), the sampling and filtering unit 150 samples and outputs the signal.

FIG. 2 is a flowchart illustrating an operation of the turnover search logic unit of FIG. 1.

As illustrated in FIG. 2, the binary search logic unit 180 assumes that the current mode DAC of the current converter 180 has an N-bit resolution.

First, in the initialization state, when the SC signal (start of conversion) rises, the system enters the initialization mode. At this time, the Most Significant Bit (MSB) is set to H, and the most significant bits (LSBs) are set to L. Settings. Then, the counter variable k is set to 0 (S110).

Subsequently, after a little time that the current-voltage conversion amplification unit 140 stabilizes, the fraud comparison unit 170 determines the sign of whether the output signal Vout of the current-voltage conversion amplification unit 140 is positive or negative. By doing so, COMP, which is an output signal of the comparator 170, is output (S120).

When the output signal COMP of the comparator 170 is H, MSB-k th bit is set to H (S130), and when the output signal COMP of the comparator 170 is L, MSB-k th bit is L Set (S140).

At this time, the size of k and N are compared (S150), and if k <N, the counter variable k is increased by 1 (S160), the MSB-k bit is set to H (S170), and the comparison operation is repeated. do.

Through this process, a binary search process is performed to find a value where the output signal Vout of the current-voltage conversion amplifier 140 is closest to zero. Thereafter, when k> N, EOC (End of Conversion) is generated as H and ends (S180).

3 is a circuit diagram illustrating the binary search logic unit of FIG. 1.

The binary search logic of the binary search logic unit 180 may be implemented in various forms, and an appropriate implementation example is a plurality of D-flipflop (DFF) serially, as shown in FIG. 3. It can be implemented by linking. At this time, the DFF array of two rows connected in series is used, and the DFF of the first row serves as a counter k in the form of a shift register.

Here, each DFF is composed of a DFF having an asynchronous SET (SET) and an asynchronous reset (RST) signal. When the SC signal becomes H, the output Q of the first DFF in the first row becomes H, and the outputs of all other DFFs become L.

On the other hand, the DFF in the second row serves to update the COMP value. When COMP = H, the COMP value is updated to DFF, and when COMP = L, the COMP value is not updated, and L is maintained.

When the last COMP signal comes in, the EOC signal finally occurs in H, indicating that the binary search has ended.

4 is an operation timing diagram of the binary logic operation unit of 3.

As shown in FIG. 4, the clock signal CLK is input to the binary search logic, and at LED_ON = L, the light emitting unit 120 is in an OFF state. When the SC signal is input, a binary search operation is started to remove the ambient current. After the ambient signal is removed by the N bit clock operation, the EOC signal is generated to signal the end of the binary search operation, and then set LED_ON = H to amplify only the PPG signal.

During the period in which LED_ON = H, the stabilization time of the current-voltage conversion amplification unit 140 is passed, and after an appropriate time delay, the output signal of the current-voltage conversion amplification unit 140 is sampled and filtered, and the digital conversion unit 160 ) To digital.

Therefore, the automatic offset calibration device based on the binary search of the oxygen saturation meter according to the present invention can automatically remove the ambient light current included in the current of the detector 130 using a simple binary search based circuit. Compared to the existing invention, the circuit structure and algorithm are simple, and since the output signal of the current-voltage conversion amplifier is directly used, a digital converter is used to convert to digital or the ambient light is faster than the existing technology that requires communication with the host processor. The current can be removed.

For this reason, the oxygen saturation meter is used for elderly people with respiratory disorders over 60 years of age, or when consciousness disorder, shock, or heart failure is confirmed. Also, people who need long-term concentration, long-distance drivers or people tired of chronic fatigue, sports When you need data about your body condition, or will be used for people with lung disease or chronic obstructive pulmonary disease.

On the other hand, the above description of the present invention is for illustration only, and those of ordinary skill in the art to which the present invention pertains understand that it is possible to easily modify to other specific forms without changing the technical spirit or essential features of the present invention. Will be able to. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the present invention is indicated by the following claims rather than the above detailed description, and it should be interpreted that all changes or modified forms derived from the meaning and scope of the claims and equivalent concepts thereof are included in the scope of the present invention. do.

110: LED driving unit 120: light emitting unit
130: detection unit 140: current-voltage conversion amplification unit
150: sampling and filtering unit 160: digital conversion unit
170: comparison unit 180: binary search logic unit
190: current converter

Claims (5)

LED driving unit for generating a current,
And a light emitting unit for emitting light receiving the current generated from the LED driving unit,
A detection unit for detecting light reflected from blood vessels inside the finger approaching the light emitting unit and converting it into current, and outputting the converted light;
A current-voltage conversion amplification unit that receives the converted current from the detection unit, converts it into a voltage, amplifies and outputs it;
A sampling and filtering unit that receives the converted and amplified voltage from the current-voltage conversion amplification unit, and samples and filters the output voltage;
A digital converter that receives the filtered voltage from the sampling and filtering unit, converts it into a digital value, and outputs it;
A comparison unit that receives the output signal of the current-voltage conversion amplification unit and compares whether it is positive or negative;
A binary search logic unit that searches for a binary search logic based on the comparison result of the comparison unit and searches for a value in which the output signal of the current-voltage conversion amplification unit approaches O;
Binary search-based automatic offset correction device for an oxygen saturation meter, characterized in that it comprises a current converter for converting the value retrieved from the binary search logic unit to an analog value and outputting it to the current-voltage conversion amplifier. According to claim 1, The binary search logic unit binary offset-based automatic offset calibration device of the oxygen saturation meter, characterized in that configured by connecting a plurality of D-flip-flop in series. The binary offset based automatic offset correction device of an oxygen saturation measuring device according to claim 2, wherein the binary search logic unit comprises a DFF array of two rows in which the plurality of D-flip flops are connected in series. 4. The automatic offset calibration device according to claim 3, wherein the DFF of the first row of the DFF array of two rows connected in series serves as a counter in the form of a shift register. 4. The automatic offset calibration device according to claim 3, wherein each of the DFFs comprises a DFF having an asynchronous set and an asynchronous reset signal.

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